The need for ground fault cirucit interrupting devices (GFCI) in certain residential electrical circuits and on construction sites to protect people from potentially injurious electrical shock is becoming well recognized as evidenced by their adoption by the National Electrical Code and OSHA. These devices respond to ground fault leakage currents of five milliamps or more to interrupt a circuit in time to prevent injurious consequences. To respond to such low level, but nevertheless hazardous, ground fault currents requires extreme sensitivity which can only be achieved using sophisticated electronic circuitry. Such ultra-sensitivity renders the GFCI device susceptible to nuisance tripping by electrical noise which is inevitably present on residential circuits in surprising abundance. Elaborate measures are necessary to counter this noise problem, in order that the GFCI device trip only with the existence of ground fault leakage current of the requisite magnitude.
In addition, the electric circuitry must be produced as a compact, essentially miniaturized module such that, when combined with circuit interrupting means, the completed device can be accommodated in existing load centers as a GFCI circuit breaker or outlet boxes as a GFCI receptacle, in the same manner as conventional circuit breakers and outlet receptacles. Such circuitry miniaturization aggravates the problems of noise, temperature variations, and instability.
It is accordingly an object of the presnt invention to provide an improved ground fault circuit interrupting (GFCI) device.
Another object of the present invention is to provide a GFCI device of the above character which incorporates an improved, ultrasensitive electronic module.
Still another object is to provide a GFCI electronic module of the above character, wherein nuisance tripping due to noise is avoided.
A further object is to provide a GFCI electronic module of the above character, which is reliable over a long operating life and is relatively inexpensive to manufacture in quantity.
Other objects of the invention will in part be obvious and in part appear hereinafter.